Self-energizing temperature control systems have been widely available for several years. These prior art systems have employed either a mechanical bi-metallic thermostat in series with a thermopile and a gas valve, or a so-called solid-state equivalent of this circuit. In this regard, U.S. Pat. Nos. 4,696,639; 4,770,629 and 4,734,658 to Bohan, Jr. disclose a solid-state version of a self-starting free running multi-vibrator to step up the low voltage of a thermoelectric device (e.g., a thermopile). The energy provided by the thermoelectric device (TED) is the sole energy source. Accordingly, in the event that the pilot flame is extinguished, or the TED fails, all power to the temperature control system is lost. Moreover, Bohan's temperature control system requires a user to manually light a standing pilot in order to initially start the system. The actuator for the manually-actuated gas valve cannot be released by the user until the TED is producing sufficient energy. Once the thermopile is up to rated output, the manually-actuated actuated valve for the standing pilot is latched open magnetically by some of the current from the TED.
An indicator light is provided to signal when the user can release the actuator for the manually-actuated gas valve. The indicator light is activated when there is sufficient power from the TED to operate the control system. Typically, the actuator will be not be released for at least three minutes after the pilot burner has been lit. If the actuator is released too soon, the gas valve will shut off and the pilot flame will go out. When this happens the whole process of pilot start-up must be repeated. The indicator light is therefore a convenience feature for the user. A system that lit off the main burner whenever the TED was operational would serve the same purpose.
Gas valves currently in use today that are operated directly by a TED have two (2) coils. One coil is a low power latching coil that is used as a safety device such that if the TED stops putting out power, the safety coil will release and the gas supply to the burners will be shut off. The second coil controls the normal ON/OFF flow of gas to the main burner. Once the standing pilot is lit it remains lit until manually shut off or until for whatever reason the TED stops providing output power. The TED may stop providing power due to the loss of the standing pilot flame and/or failure of the TED itself. If the TED stops providing power, then the safety coil will drop out and the gas flow to burner and pilot will stop. Safety issues are paramount whenever a gas-fired system is being controlled. A dangerous situation will develop anytime gas flows and there is no combustion taking place. Accordingly, it is imperative that the gas flow to a burner and pilot is stopped anytime the burner or pilot flame goes out.
The present invention addresses these and other drawbacks of prior art temperature control systems, to provide a temperature control system with greater reliability, safety and efficiency.